Storage tanks

ABSTRACT

1,123,254. Liquefied gas storage tanks. WHESSOE Ltd. 30 June, 1966 [1 July, 1965], No. 27978/65. Heading F4P. The flat bottom 1 of a liquefied gas storage container is supported on a layer of granular heat insulating material 3, e.g. gravel, which extends outwardly beyond the periphery of the base and which is protected from ambient moisture by a layer 7 of asphalt. The roof and vertical cylindrical wall 2 of the container is lagged with heat insulation material 8 wrapped with an impervious cover 8a. The gravel 3 and asphalt 7 are retained within a steel tray 4 provided with a steam-heated tube 6. In a modification, the tray is of concrete supported by piles or by a continuous slab of concrete. The cylinder wall 2 has a plurality of peripherally spaced brackets (11), Fig. 3 (not shown), each engaged by a holding-down bolt (13) extending downwardly through a sleeve (14) in gravel layer 3 and pivoted to anchor bolts (15).

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ATTQRNEYS United States Patent O 3,448,886 STORAGE TANKS Gordon Todd and Edward Francis Shields, Stockton-ou- Tees, Durham, England, assignors to Whessoe Limited Filed June 30, 1966, Ser. No. 561,981 Claims priority, application Great Britain, July 1, 1965, 27,978/65 Int. Cl. B65d 25/18 U.S. Cl. 220-9 5 Claims ABSTRACT F THE DISCLOSURE A tank for storing cold liquids which is supported on a layer of loose, divided insulating material contained in a tray to avoid spreading of the material, said tray having means to protect it against the ingress of moisture.

This invention relates to tanks for the storage of liquids at temperatures below the ambient temperature, including in particular tanks intended for the bulk storage of liquefied petroleum gases at pressures not greatly in excess of atmospheric pressure.

The general object of the invention is to provide an improved manner of supporting and insulating the base of a tank intended for the above purpose. Such tanks may be of very large dimensions, for example up to 180 feet or more in diameter and 70 feet or more in height.

An installation in accordance with the present invention for the storage of liquid at a temperature below the ambient temperature comprises a tank for containing liquid to be stored, said tank having a at base, a peripheral wall extending upwardly from said base and a roof.

covering the space enclosed by said wall, a layer of heat insulating material in divided form which underlies the base of the tank and extends outwardly beyond the periphery of said base, the tank resting on and being supported by said layer, and means for preventing access of moisture to said layer of heat insulating material. The depth of the layer of insulating material is chosen in accordance with the operating temperature and the thermal properties of the insulating material. The insulating material may be a foamed slag aggregate, or other low cost material in a divided form, such as sand or washed gravel, having adequate compressivestrength and insulating properties.

The layer of heat insulating material on which the tank is supported is preferably contained within a tray having a base underlying and supporting said layer and a peripheral wall upstanding from said base and preventing outward lateral spread of said insulating material. The tray may be constructed from steel, or from concrete, reinforced or not; it may be cast in concrete as an integral part of the base foundation, or may be formed directly in the ground. If the tank is of double skin construction, the lower part of the outer tank may constitute the tray containing the layer of insulating material on which is supported the inner tank in which the liquid is stored.

Whatever its construction, the tray in which the layer of heat insulating material is contained may be supported in elevated position so as to afford an air gap beneath the tray and thereby reduce the flow of heat between tray and ground. If the tray is in contact with the ground, either directly or through the foundations (Le. if there is no air gap between the tray and the ground), the presence in the tank of liquid at sub-zero temperature could cause Ifreezing of the natural moisture present in the area of ground immediately below the tank, resulting in frost heave. This can be prevented by incorporating suitable heating means in the ice tray to ensure that the :ground area immediately below the tank does not fall .to sub-zero temperatures.

To prevent the access of moisture to the layer of heat insulating material, the top surface of the insulating material, or at least that part of the surface which extends outwardly beyond the tank base, may be covered with a bitumen/ sand mixture, asphalt or other moisture-impervious layer. Such a layer prevents the penetration of water or water vapour into the insulating material during the period when the tank is being constructed and during operation. A temporary cover of any suitable character can be employed to exclude water from the tray during the period when the insulating material itself is being placed in position, but the provision of such a cover may be unnecessary if washed gravel, or other material having free draining characteristics, is used as an insulating material, and adequate arrangements are made for keeping the tray drained. Additionally, if so desired, the above mentioned heating means could be used to reduce the amount of moisture in the insulating material prior to commissioning.

Particular embodiments of the invention Iare illustrated in the accompanying drawing, in which:

FIGURE 1 is a diagrammatic representation of a vertical section through a storage tank in accordance with the invention;

FIGURE 2 is a similar view of an alternative construction;

FIGURE 3 is a vertical sectional view of an enlarged scale of a detail; and

FIGURE 4 is a view similar in character to FIGURES 1 and 2 of another alternative construction;

The same reference numerals are used to designate corresponding parts in the several figures of the drawing.

In the construction shown in FIGURE l, the base 1 of a vertical cylindrical storage tank 2 of conventional construction rests on a layer of washed gravel or other insulating material 3 contained in a fabricated steel tray 4. The tray 4 is shown as resting directly on the surface of the ground 5, which is assumed to have good load bearing properties, so that no special foundation provisions are required. Embedded in the insulating material in the tray and heating means 6, which may be coils for the circulation of steam, hot water, hot oil or other heating fluid, or may be electrical heating devices. The upper surface of the insulating material is covered by a layer 7 of asphalt or other material impervious to water and water vapour, which serves to keep out moisture from the insulating material 3 during the period when the storage tank is being constructed and also subsequently during operation. The roof and walls of tank 1 are provided externally with heat insulation 8 having a covering (indicated by chain line 8a) which is impervious to water and water vapour. This covering 8a is extended outwardly as shown to cover the projecting margin of the layer of insulating material 3 and the tray in which it is contained, the covering 8a being sealed to tray 4. Alternatively, the moistureimpervious covering 8a may be sealed to the moistureimpervious layer 7.

The construction shown in FIGURE Z is generally similar to that of FIGURE 1, but in this case the tray 4 is shown as made from concrete and as supported on piles 9, leaving an air gap between the underside of the tray and the surface of the ground 5. Such a reinforced concrete tray may, of course, rest directly on the ground, as shown in FIGURE 1, or be embedded in it, while a steel tray as shown in FIGURE 1 may be supported in elevated position, as shown in FIGURE 2.

The storage tank may be secured to its foundations by holding down bolts for resisting the effect of upthrust resulting from the Working pressure in the tank. One

possible arrangement of such bolts is shown in FIGURE 3. In this case, the fabricated steel tray 4 which contains the layer of insulating material 3 rests on a concrete foundation slab 10. Brackets 11 secured at intervals to the wall of the tank 2 are engaged (with the interposition of insulating washers 12) by the upper ends of holding down bolts 13, which pass downwardly through sleeves 14 in the insulating material 3. The lower ends of the bolts 13 are attached pivotally (to allow for radial expansion movements of the tank) to anchorage members 15 secured in the foundation slab 10. When no foundation slab is provided, as in FIGURE 1, the holding down bolts may be anchored to individual concrete blocks set into the ground below the tray. When a tray of reinforced concrete is employed, the tray itself may serve as a foundation slab, the holding down bolts being anchored to the tray itself.

FIGURE 4 illustrates one manner of applying the invention to a double skin refrigerated storage tank. The stored liquid is containing in the inner tank, whose base 1 rests on and is supported by the layer 3 of heat insulating material, which is in turn supported on the base 17 of the outer tank and is confined by the wall 16 of that tank. In the gure, the base of the outer tank is shown as resting ou a platform 18, supported above the ground 5 by piles 9, but in suitable cases it may rest directly on the ground, or any other form of foundation may be employed. During operation of the storage installation, the outer tank alone is sufficient to prevent any access of moisture to the heat insulating layer 3. To prevent such access during the construction of the installation, a layer 7 of `moisture-impervious material may be provided, but if the outer tank is built rst (the inner tank being subsequently erected within it) the provision of such a layer may be unnecessary.

What is claimed is:

1. In an installation for the storage of liquid at a temperature below the ambient temperature, a tank for containing said liquid, said tank having a fiat base, an exterior peripheral wall extending upwardly from said base and a roof covering the space enclosed by said wall, a layer upon which said wall is supported, said layer consisting essentially of at least one loose insulating material in divided form, said material being selected from the group consisting of foamed slag aggregate, sand and gravel, and said layer extending outwardly beyond the periphery of said wall, a tray containing said material and having a peripheral wall which prevents lateral spreading of said insulating material, said tray being supported in an elevated position with an airspace beneath the base of said tray, and means for preventing the access of moisture to said material, said means including a layer of moisture impervious material covering that part of the upper surface of said layer which extends beyond the exterior wall of said tank.

2. An installation in accordance with claim 1, in which the wall and roof of the tank are provided externally with heat insulation having a moisture-impervious covering, and said covering is sealed moisture tight to the wall of the tray.

3. An installation in accordance with claim 1, in which the wall and roof of the tank are provided externally with heat insulation having a moisture-impervious covering, and said covering is sealed moisture-tight to said layer of moisture impervious material.

4. An installation in accordance with claim 1, in which a plurality of brackets is secured externally to the wall of the tank at intervals around its periphery and each of said brackets is engaged by a holding-down bolt which extends downwardly through a sleeve embedded in said layer of heat insulating material and is pivotally attached at its lower end to a secure anchorage.

S. An installation in accordance with claim 1, in which said tray is constituted by the lower part of a second tank, which surrounds the said tank for containing liquid to be stored.

References Cited UNITED STATES PATENTS 2,520,883 8/1950 Kornemann et al. 2,655,255 10/1953 Brown 220-10 X 2,924,352 2/1960 Santner et al 220--18 3,047,184 7/1962 Van Bergen et al. 3,076,317 2/1963 La Fave.

3,196,622 7/1965 Smith et al. 3,274,785 9/1966 Lange. 3,339,779 9/1967 Horton et al.

FOREIGN PATENTS 1,030,858 5/1966 Great Britain.

JOSEPH R. LECLAIR, Primary Examiner.

JAMES R. GARRE'IT, Assistant Examiner.

U.S. Cl. X.R. 220-18 

